Do you think, that the availability of the boss in the company bring's tense and nervous atmosphere to the employees?

No, perhaps it is good for the employee if the boss is always in the office, in a way that they can ask question if there is situation that they cannot decide by their own.

its depend upon the atmosphere of the office.
boss is to be there to check up the follow up done by employees.
its is required to see offenly the bright side of the phase.

NO , it brings pleaseure for the employess to handle the situation when there is a issue comes, Boss will guide his team what to do and what not to do

not at all.some bosses they are pleasant and easy to communicate with their people.

Definitely yes, but in general it should have been all rank and files in company should undergo training as to the emergency response.